1. Field of the Invention
The present invention relates generally to wafer carriers. More particularly, the present invention relates to systems for ensuring that such carriers are suitable for use.
2. Description of Related Art
Wafer carriers (or, as they are also called, "boats" or "cassettes") have been used for many years in the electronic arts, particularly the semiconductor arts, to support wafers during processing. Typical wafer carriers are described, for example, in U.S. Pat. Nos. 4,993,559; 4,355,974; 4,256,229; 4,515,104; 3,678,893; 3,534,862; 4,023,691; and 3,610,613, which are all incorporated herein by this reference thereto. Generally, such carriers are constructed so as to form a multitude of slots into which wafers may be placed for transport and processing. Quartz is a common construction material for wafer carriers that are intended for use in high temperature processes; in most other circumstances, plastic is the preferred construction material because it is relatively inexpensive and easy to work with. Other materials are also used.
The processing of wafers to make integrated circuit chips requires that they be successively immersed, sprayed and/or rinsed with liquids or gases. Some of the chemical baths include corrosive chemicals. Some involve very high temperatures.
Wafer carriers can, over the course of time, and after a multitude of processing cycles, become warped or worn. Warped, excessively worn, or other such flawed carriers can cause manufacturing problems. For example, if slots come to vary in size or in the amounts of inclination they allow wafers, the degree of exposure of different wafers in the same carrier to various processing agents can differ. This, in turn, can lead to undesirable manufacturing variances. Another major problem that can arise when damaged or warped boats are used relates to automated handling. Robots on assembly lines may not adjust to equipment that falls outside of prescribed tolerances. For example, if a robot is programmed to pick up a boat at a prescribed location, and if that boat is damaged or warped, there is a strong possibility that the boat will be mishandled by the robot. Because robots often travel at high rates of speed, mishandling damage can be severe, and can include chipped wafers, wafers with stress fractures, and even broken wafers. Damages can be exacerbated by one damaged wafer contaminating a multitude of surrounding wafers. One single mishandling incident can easily cause hundreds of thousands of dollars worth of damage.
Based upon the foregoing, it should be understood and appreciated that it is important that plastic boats and other such wafer carriers be checked periodically to ensure that they fall within prescribed tolerances. Although there has been made some developments made in slot size checking apparatus and methods for such boats; for example, those skilled in the art have heretofore measured slot width with plug gauges, calipers, and the like, and they have also developed complex measuring systems using lasers; the art has heretofore lacked an inexpensive apparatus and method for quicking and easily checking plastic boats and the like to ensure that they remain structurally suitable for use. It is a shortcoming and deficiency of the prior art that there has not heretofore been such an apparatus or method.